A large number of wheeled or tracked platform mechanisms have been studied and developed to provide their mobility capability to teleooperated and autonomous robot vehicles. For large and heavy outdoor robots, four-wheel, car-like driving mechanisms or skid-steer platforms have traditionally been used. Because of kinematic constraints, these vehicles are restricted in their motion in the sense that they cannot move sideways (also known as "crab motion") without preliminary maneuvering. Better motion capabilities have been investigated in a variety of research centers and demonstrated on smaller laboratory robots. These improvements in motion capabilities typically are derived from the use of two independent driving wheels supplemented by casters, or by three steerable and coordinated driving wheels. The former type allows rotation of the platform around any point but does not allow sideways motion, while the later type realizes both rotation of the platform and sideways motion through coordinated steering of the wheels.
With the aforementioned three wheeled platform rotation and translation cannot occur simultaneously. Moreover, steering requires rotation of the wheels around a vertical axis which, for larger vehicles equipped with wide tires, may generate significant sliding and friction of the wheels.
Other structures of interest include the following: U.S. Pat. No. 3,912,037 to Krieg describes a transport vehicle having wheels that are pivotal for guidance. At least one vehicle carries an induction sensitive probe; U.S. Pat. No. 4,237,990 to La describes an omni-directional vehicle which has three individually driven wheels rotatable about horizontal axes, such that the wheels are arranged in a triangle; U.S. Pat. No. 4,463,821 to Falamak describes a steerable platform having wheels mounted on rotatable casters, and a control circuit which includes a transmitter, a receiver, steering sensors, and driving/steering clutches; U.S. Pat. No. 4,223,753 to Bradbury describes an omni-directional transport device in which driving wheels are disposed in pairs of side-by-side flat-sided spheres drivingly interconnected with the sides of one sphere turned 90.degree. to the sides of the other; and U.S. Pat. No. 4,972,917 to Matsumoto et al. describes a carriage in which three wheels are driven and steerable to effect sideways and spin-turn motion.
None of the aforementioned devices succeed in fully decoupling the rotational and translational degrees of freedom while providing an omni-directional capability to the platform.